Tone audiogram

from Wikipedia, the free encyclopedia

A tone audiogram ( pure tone audiogram ( RTA ), hearing curve or audiogram for short ) is created by measuring the subjective hearing ability for tones, i.e. the frequency-dependent hearing sensitivity of a person, the test person .

Recording an audiogram

As a method of audiometry, it is an important diagnostic tool in ear, nose and throat medicine . With a tone audiogram, statements can be made about the symptoms and sometimes also about the causes of hearing impairments. Deviations from the norm in the audiogram suggest a disease of the ear .

Creation of a tone audiogram

Tone Audiogram Form

The participation of the test person is necessary to record a tone audiogram. The examiner plays certain tones one after the other in increasing volume via headphones or bone conduction headphones , and for certain questions also via loudspeakers . Most tone audiometers increase the volume in 5 decibel steps. The test person gives the agreed signal (usually by pressing a button) as soon as he hears the tone. This process is repeated until the hearing threshold is precisely determined. The examination is performed for both air conduction and bone conduction .

The determined decibel value is entered in a standardized form as the hearing threshold for each tested pitch . The horizontal axis of this form shows the pitch ( frequency in Hertz or Kilohertz). The vertical axis indicates - increasing from top to bottom - the volume in decibels at which the hearing threshold is. The designation of the unit of measurement is dBHL (like Hearing Level ), since a sound pressure level is specified; the line at 0 dBHL corresponds to the standardized reference value p 0 , which is close to the hearing threshold of a healthy subject. Uniform characters are entered in the form for the results, namely for air conduction right “o”, left “x”, for bone conduction right “>” and left “<”.

For this purpose, the standard DIN EN ISO 8253 "Audiometric test methods" is available as the standard for implementation.

Statement of a tone audiogram

A tone audiogram indicates the air conduction hearing threshold (conduction of sound signals via the outer ear) and bone conduction hearing threshold (conduction of sound signals via the skull bones) at the different frequencies (pitches). If the air conduction hearing threshold is normal, the ossicles, sensory cells in the cochlea and the auditory nerve work normally.

In the case of a sound sensation disorder, the air conduction and bone conduction hearing threshold are in the same way at higher decibel values ​​than in normal hearing people. If, on the other hand, sounds are poorly perceived via air conduction but normal via bone conduction, this is a sound conduction disorder . Both types of hearing loss can be present at the same time; then the bone conduction hearing threshold is worse than normal, but the air conduction hearing threshold is even worse. One then speaks of a combined hearing loss .

Sound sources for tone audiograms

Headphones are used to measure air conduction and loudspeakers are used for certain questions (free field audiometry). The investigation must be carried out in a soundproofed, anechoic room, usually a soundproof cabin, in order to exclude background noise.

A bone conduction receiver is used to measure the function of the inner ear in isolation. In principle, a bone conduction receiver is a loudspeaker that does not have a membrane so that it cannot radiate sound through the air. It is placed on the skull ( mastoid process ) on the side of the ear to be examined and thus transfers the vibrations to the bones and directly to the inner ear.

Since the sound spreads over the entire skull when measuring with a bone conduction receiver, the opposite ear hears a significant proportion of the signal offered. For this reason, if the hearing sensitivity of the ears is different, the ear that has not been tested and which has better hearing is "deafened" (deadening) with a loud noise from headphones, so that only the other ear can perceive the sounds. If there are very large differences between the sides, the ear that has not been tested must also be masked when testing with headphones.

Reliability of the result

The examination is dependent on the cooperation of the person examined. People who are overwhelmed with the task (e.g. smaller children) cannot be examined this way. It is also possible for a patient to aggravate , i.e. to depict existing symptoms worse than they are, or to simulate them at all . For a rough assessment of the hearing ability of non-cooperative persons, similar to the newborn hearing screening , early acoustic evoked potentials can be used.

Differentiation according to sequence and tone sequence

There are several ways to record a tone audiogram. They differ primarily in the sequence in which the sound stimuli are presented to the test person and how the test person should react to them.

The simplest method is to play a tone below the normal hearing threshold and then increase the level until the test person confirms the perception. In order to exclude uncertainties, the procedure is usually repeated for each tone. This method can be used to record discrete hearing thresholds for individual frequencies.

Less common, as it is relatively time-consuming, is Békésy tracking , in which the pitch is continuously increased and the test subject can decrease or increase the level by pressing or releasing a key. As with most other procedures, he is only instructed to press the button when he hears it. Since the test person has no way of keeping the level constant, the audiogram shows a characteristic, close-meshed zigzag line that alternately falls below and exceeds the actual hearing threshold.

Examples

  • Tone audiogram, normal hearing

  • Tone audiogram, conduction disorder

  • Tone audiogram, sensorineural sensation disorder

  • Tone audiogram, combined hearing loss

Typical pathological findings in audiometry are:

  • Tub-shaped depression of the bone conduction threshold curve in the range of 2 kHz ( Carhart depression) with simultaneous acoustic conduction disorder and normal eardrum findings, characteristic of otosclerosis ,
  • Depression in the low and medium frequency range (bass hearing loss, "hydrops curve") (sensorineural hearing loss), characteristic of Menière's disease ,
  • Decrease in high frequencies (sensorineural hearing loss), often in presbycusis (old age hearing loss ),
  • C 5 (approx. 4000 Hz) -sink ( sensorineural hearing loss ), characteristic of noise- induced hearing loss .

Individual evidence

  1. ↑ DIN EN ISO 8253 "Audiometric test methods", Part 1: Basic methods of air and bone conduction threshold audiometry with pure tones and Part 2: Sound field audiometry with pure tones and narrow-band test signals, Beuth-Verlag Berlin
  2. ↑ Hans-Georg Boenninghaus and Thomas Lenarz : Ear, Nose and Throat Medicine . 13th edition. Springer, Heidelberg 2007, ISBN 978-3-540-48721-0 .

See also

Web links